1. Field of the Invention
Embodiments of the invention generally relate to the field of hard disk drives. More specifically embodiments of the invention relate methods and apparatus to control lubrication migration on head sliders in hard disk drives.
2. Description of the Related Art
Hard disk drives are used in many computer system operations. In fact, many computing systems operate with some type of hard disk drive to store the most basic computing information, e.g., the boot operation, the operating system, the applications, etc. In general, the hard disk drive is a device, which may or may not be removable, but without which, some computing systems may not operate.
One basic hard disk drive model was developed approximately 40 years ago and in some ways resembles a phonograph type apparatus. For instance, the hard drive model includes a storage disk or hard disk that spins at a standard rotational speed. An actuator arm or slider is utilized to reach out over the disk. The arm has a magnetic read/write transducer or head for reading/writing information to or from a location on the disk. The complete assembly, e.g., the arm and head, is called a head gimbal assembly (HGA). The assembly consisting of the disks, HGAs, spindle, housing, and the other parts internal to the housing is called the head disk assembly, or HDA.
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are channels or tracks spaced at known intervals across the disk. Most current embodiments arrange the signal regions in concentric circular tracks, but other designs, such as spirals or irregular closed or open paths are possible and useful. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk. Refinement of the disk and the head have provided reductions in the size of the hard disk drive. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches.
The ever increasing need for data storage has led some disk drive makers to steadily increase the amount of data stored on a drive. Mechanical considerations, radiated audible noise limits, power requirements, and other factors limit the number of disks that can be economically combined in a single drive. Thus, disk drive technology has generally focused on increasing the amount of data stored on each disk surface by positioning the heads more closely to the media surface. However, care must be taken to avoid unintended contact between the head components and the moving media surface.
Typically, the heads are lightly spring loaded, with the spring tension perpendicular to the media surface plane and directed against the media surface. An air bearing separates the head and media surfaces as follows: As the media moves relative to the head, air is dragged by the disk surface through specifically designed channels in the surface of the head adjacent to the media surface. The surface of the head and the channels contained therein, collectively referred to as the air-bearing surface (ABS), are designed to generate regions of increased air pressure in between the ABS and media surface that forces the head away from direct contact with the media surface, in effect causing the head to fly above the media surface. The separation of the head ABS and media surface, commonly called fly height, is a complex phenomenon that is primarily a function of air density, the spring preload, the relative speed between the head and media surface, and the pattern of channels present on the head air bearing surface adjacent to the media surface. It is well known to those familiar with head-disk interface design that a particular head-disk combination will not fly precisely at the desired separation. Variances in mechanical tolerances, spring tensions, and other factors result in a nearly normal statistical fly-height population distribution generally centered about the mean fly height. Furthermore, the head and its mounting gimbal are subject to mechanical tolerances, aerodynamic forces, and inertial forces that can cause it to deviate from the desired altitude with respect to the media surface, (e.g. static and dynamic pitch and roll). This can move some areas of the air bearing surface closer or further from the media surface.